Radiative Decays of Heavy Mesons and the Determination of the Strong g-Coupling

The strong g-coupling characterizes the interaction of heavy mesons with pions in typical vertices $H^*H\pi$, $H^*H^*\pi$, where $(H^*;H)$ stands for vector and pseudoscalar $(B^*;B)$ or $(D^*;D)$ heavy mesons. Its estimation by different theoretical methods has led to a wide range of possible values. We describe a new approach to the determination of g, which exploits the rare radiative decays $B^*\to B\gamma\gamma$ and $D^*\to D\gamma\gamma$. It is shown that the branching ratio of $D^*\to D\gamma\gamma$ can be expressed as a function of a single unknown $g$ and we calculate it to be in the measurable range between $1.6\times 10^{-6}$ and $3.3\times 10^{-5}$ for 0.25 < g < 1.